Process for preparing substituted benzoyl chlorides

ABSTRACT

The present invention relates to a process for preparing substituted benzoyl chlorides of the formula (1) 
                 
 
where R, x and y have the meaning given below, which comprises reacting a benzaldehyde of the formula (2) 
                 
 
where R, independently of each other, is identical or different and is an unsubstituted phenyl radical or a phenyl radical that is substituted by halogen, NO 2 , CN, (C 1 -C 4 )alkyl or (C 1 -C 4 )alkoxy, or is halogen, NO 2 , CN, NR′ 2 , OR′, SO 2 R′, SO 2 OR′, COR′ or CO 2 R′, where R′ is an unbranched or branched C 1 -C 10  alkyl radical, an unsubstituted phenyl radical or a phenyl radical which is substituted by halogen, NO 2 , CN, (C 1 -C 4 )alkyl or (C 1 -C 4 )alkoxy, x is 1 or 2 and y is 1, 2 or 3, with a chlorinating agent in the presence of a free-radical initiator and a solvent at from −20 to +200° C.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation in part of U.S. Ser. No. 09/915,830,filed Jul. 26, 2001 now abandoned, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a process for preparing substitutedbenzoyl chlorides by chlorinating the corresponding benzaldehydes.Substituted benzoyl chlorides may be considered activated derivatives ofthe corresponding benzoic acids. For this reason they are widely used asvaluable synthesis building blocks, for example as intermediates forproducing plant protection agents and drugs and for producing dyes andplastics.

Aromatic carboxylic acid chlorides are customarily prepared by reactingcarboxylic acids with a chlorinating agent or by partial hydrolysis ofbenzotrichlorides. An important advantage of these processes is based onthe fact that the corresponding starting materials are available on anindustrial scale, because they are easily accessible. These favorablepreconditions are not present in the case of preparation of substitutedbenzoyl chlorides, since the corresponding starting materials, i.e.appropriately substituted carboxylic acids or benzotrichlorides aregenerally not readily accessible and also are not usually available inindustrial quantities.

It is known that starting from aldehydes, by halogenating the aldehydegroup, carboxylic acid halides are accessible directly.

SUMMARY OF THE INVENTION

Thus EP 0 723 950 B1 describes a process for preparing alkylbenzoylchlorides by chlorinating alkylbenzaldehydes. Although in this case thereaction is carried out in the presence of a solvent and a furthermethyl- or chloromethyl-substituted benzene derivative, the selectivitynever exceeds 86%. Owing to the use of a complex mixture of substances(at least 4 components) and the not very high selectivities,purification of the reaction product is very costly and the productquality is adversely affected.

The reaction of alkylbenzaldehydes with chlorine in the presence of asolvent and an inert gas leads only to moderate selectivities of benzoylchlorides (see example 3 in EP 0 849 253 A1:81%). As a result, itsability to be carried out industrially becomes uneconomic.

A process for preparing 3-chloro-4-fluorobenzoyl chloride is describedin EP 0 922 693 A1. In this case the precursor 4-fluorobenzoyl chlorideis prepared by chlorinating 4-fluorobenzaldehyde. However, 8.3% of aminor component are also formed, (they are identified as4,4′-difluorobenzil) which makes purifying the product more difficult.When 4-fluorobenzaldehyde is chlorinated in the absence of a solvent, agel-like solid forms with intensive foam formation (see comparativeexample 3 in the experimental part). A further disadvantage is thesignificantly increased formation of a chlorine byproduct (no4,4′-difluorobenzil) and the associated markedly worsened selectivity.

The use of ortho-halo-substituted benzaldehydes, i.e.2-halo-benzaldehydes (in which a halogen is in the ortho position to thealdehyde group) gives an additional problem. This is because thesealdehydes have a tendency in part to dehalogenate (see comparativeexample 1a in the experimental part), which forms products which arefrequently very difficult to separate off and thus adversely affect thequality of the end products, which is subject to very high requirementsfor use in the syntheses for pharmaceutical products or plant protectionagents.

Furthermore, in the chlorination, one or more byproducts (termed minorcomponents in the experimental part) are frequently formed, which areassumed to be secondary products of uncontrolled reactions between thebenzoyl chloride prepared and still unreacted starting product(substituted benzaldehyde), possibly with the participation of chlorine.In particular, a chlorinated byproduct is formed. As shown incomparative examples 1a, 1b, 2a and 2b, this adversely affects theselectivity of the reaction.

In view of the above described disadvantages and problems, there is aneed to provide a process which avoids these disadvantages and problemsand which, without requiring great additional expense, may beimplemented in a simple manner and which makes the desired productsaccessible in high yields with high conversion rate and highselectivity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This object is surprisingly achieved by a process for preparingsubstituted benzoyl chlorides of the formula (1)

where R, x and y have the meaning given below, which comprises reactinga benzaldehyde of the formula (2)

where R, independently of each other, is identical or different and isan unsubstituted phenyl radical or a phenyl radical that is substitutedby halogen, NO₂, CN, (C₁-C₄)alkyl or (C₁-C₄)alkoxy, or is halogen, NO₂,CN, NR′₂, OR′, SO₂R′, SO₂OR′, COR′ or CO₂R′, where R′ is an unbranchedor branched C₁-C₁₀ alkyl radical, an unsubstituted phenyl radical or aphenyl radical which is substituted by halogen, NO₂, CN, (C₁-C₄)alkyl or(C₁-C₄)alkoxy, x is 1 or 2 and y is 1, 2 or 3, with a chlorinating agentin the presence of a free-radical initiator and a solvent at from −20 to+200° C.

R, x and y thus have the same meaning in formula (1) as in formula (2).

The inventive process has a plurality of advantages. Firstly, it may beapplied to a relatively large number of substituted benzaldehydes, andsecondly it is surprisingly possible to carry out the reaction withgreat success even at comparatively low temperatures (see examples 1 to4). The low temperatures make a particularly gentle reaction possible,which is of particular advantage for sensitive benzaldehydes, forexample for halogenated benzaldehydes having a tendency to dehalogenate.Although it is possible by employing low temperatures to effectivelydecrease the dehalogenation, even in the absence of a solvent (seecomparative examples 1b, 2a and 2b), the formation of unwantedbyproducts, identified as minor components, cannot be decreased to thedesired extent. As shown by a comparison between comparative example 1band example 1, and between comparative example 2b and example 2, theinventive procedure (in the presence of a solvent) leads to asurprisingly high reduction of the unwanted byproducts, which form inonly negligible amounts. A similar result can also be seen incomparative example 3 and example 3, where the formation of the minorcomponents can be reduced to roughly one-tenth of the value formed incomparative example 3. Here also there is a drastic reduction inunwanted byproducts, identified as minor components.

As examples 5, 6 and 7 prove, benzaldehydes which are halogenated orthoto the aldehyde group may be reacted even at relatively hightemperatures, at which no dehalogenation occurs and in addition unwantedbyproducts are formed only to a slight or very slight extent.

In the inventive process, very successfully, a benzaldehyde of theformula (2) may be used, where R, independently of each other, isidentical or different and is halogen, NO₂, CN, NR′₂, OR′, SO₂R′,SO₂OR′, COR′ or CO₂R′, where R′ is an unbranched or branched C₁-₄ alkylradical or an unsubstituted phenyl radical.

In particular, a benzaldehyde of the formula (2), can be used, where Rindependently of one another is identical or different and is halogen,NO₂, CN, OR′ or COR′, where R′ is an unbranched or branched C₁-C₄ alkylradical or an unsubstituted phenyl radical.

Particular interest is attached to benzaldehydes (2) where x is 1.

Interest is in addition attached to benzaldehydes (2) where y is 1 or 2,or 2 or 3, in particular where y is 1 or 2, preferably 2.

Also, a benzaldehyde (2) can be used very successfully where at leastone of the radicals R is a halogen, in particular F, Cl or Br,preferably F or Cl, in an ortho position to an aldehyde group, inparticular where one of the radicals R is a halogen in an ortho positionto an aldehyde group and a second of the radicals R is also halogen andhalogen is F, Cl or Br, in particular F or Cl.

A highly suitable benzaldehyde (2) is where R, independently of eachother, is identical or different and is F, C₁ or NO₂, x is 1 and atleast one of the radicals R is an F or Cl in an ortho position to analdehyde group.

Customarily, the substituted benzaldehyde (2) and the chlorinating agentare used in a molar ratio of 1:(0.5 to 2.0), in particular 1:(0.7 to1.5), preferably 1:(0.9 to 1.2).

The chlorinating agent can be chlorine, or a chlorine-releasing agent,in the presence or absence of an inert dilution gas such as nitrogen,carbon dioxide, or a noble gas. Preferably, the procedure is carried outin the absence of an inert dilution gas. Surprisingly when the reactionis carried out in the absence of an inert dilution gas the selectivityand conversion rate is very high see examples 8 through 12. Suitablechlorinating agents, without making any claim to completeness, are Cl₂,SOCl₂, SO₂Cl₂, PCl₃, POCl₃, PCl₅, SbCl₅, ICl, ICl₃, SCl₂, S₂Cl₂, MnCl₄,(C₁-C₄)alkylhypochlorite, CCl₄ and N-chlorosuccinimide or a mixture ofsame.

The procedure can be carried out in the presence of an inert dilutiongas. When the reaction is carried out in an inert dilution gas theselectivity and conversion rate remain good see examples 1 through 7.

In particular, Cl₂, SOCl₂, SO₂CO₂ or a mixture of same are used aschlorinating agents.

It has proved to be particularly expedient to react the substitutedbenzaldehyde (2) with Cl₂ as chlorinating agent.

Substituted benzaldehydes are reacted with the chlorinating agent in amanner of a free-radical chlorination, the presence of a free-radicalinitiator being advantageous. Usually, a peroxide or an azo compound isused individually, or in combination with one another, as free-radicalinitiator. It is known that organic peroxides and organic azo compoundsdecompose under the effects of heat and/or light into free radicals,which initiate the free-radical chlorination.

Examples of suitable peroxides and organic azo compounds are, withoutmaking any claim to completeness, ethyl methyl ketone peroxide,tert-butyl hydroperoxide, tert-butyl trimethylsilyl peroxide, cumenehydroperoxide, lauroyl peroxide, dibenzoyl peroxide, ditert-butylperoxide, dilauryl peroxide, perbenzoic acid tert-butyl ester,tert-butyl peroxy-2-ethylhexanoate,2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobis(isobutyronitrile),dimethyl-2,2′-azobis(isobutyrate), 2,2′-azobis(2-methylbutyronitrile),1,1′-azobis(1-cyclohexanecarbonitrile),2-(carbamoylazo)isobutyronitrile, 2,2′-azobis(2,4,4-trimethylpentane),2,2′-azobis(isobutyroamidine) dihydrochloride,2,2′-azobis(N,N′-dimethylenisobutyroamidine) dihydrochloride,2,2′-azobis(2-amidinopropane) dihydrochloride,2,2′-azobis(N,N′-dimethylenisobutyroamidine),4,4′-azobis(4-cyanopentanoic acid) and/or2,2′-azobis[2-methyl-N-(2-hydroxyethyl)propionamide], in particulartert-butyl hydroperoxide, dibenzoyl peroxide, dilauryl peroxide,tert-butyl peroxy-2-ethylhexanoate,2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile) and/or2,2′-azobis(isobutyronitrile).

According to a preferred variant,2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobis(isobutyronitrile)and/or 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) are used asfree-radical initiators.

The free-radical initiator (peroxide and/or azo compound) is usuallyused in an amount of from 0.001 to 10, in particular from 0.005 to 5,preferably from 0.02 to 2 mol percent, based on the substitutedbenzaldehyde (2).

The substituted benzaldehydes (2) are reacted with the chlorinatingagent in the presence of a solvent which is inert under reactionconditions. The solvent used is a monochlorinated or polychlorinatedaliphatic or aromatic hydrocarbon or a mixture of same. Examples ofsuitable solvents are, without making a claim to completeness,1,2-dichloroethane, methyl chloride, methylene chloride, chloroform,carbon tetrachloride, chlorobenzene, dichlorobenzenes, trichlorobenzenesand chlorotoluenes.

The solvent used is in particular chlorobenzene, 1,2-dichlorobenzene,1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene,1,2,4-trichlorobenzene, 1,3,5-trichlorobenzene, 2-chlorotoluene,3-chlorotoluene, 4-chlorotoluene or a mixture of the same, preferablychlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene,1,4-dichlorobenzene or a mixture of the same.

According to a particularly preferred variant, chlorobenzene is used assolvent. The solvent is usually used in a ratio of from 50:1 to 1:50, inparticular from 10:1 to 1:10, preferably from 4:1 to 1:4, based on thesubstituted benzaldehyde.

In a multiplicity of cases it has proved to be sufficient to react thesubstituted benzaldehydes (2) with the chlorinating agent at from −10 to130° C., in particular at from 0 to 120° C., preferably from 20 to 90°C., particularly preferably from 30 to 85° C.

A multiplicity of substituted benzaldehydes may be reacted verysuccessfully at a temperature of from 35 to 80° C.

The resultant substituted benzoyl chlorides (1) can be isolated byconventional workup processes which depend on the melting and boilingpoints of the products or, when employing solvents, on the solubility ofthe product in the solvent used and, in turn, on its meltingpoint/boiling point. Usual workup processes in this case arechromatography, filtration, phase separation, centrifugation ordistillation at atmospheric pressure or under reduced pressure. Inparticular, work up by distillation is the method of choice forsubstituted benzoyl chlorides.

The inventive process may be carried out batchwise or continuously. Allprocess steps can be carried out at atmospheric pressure, reducedpressure or superatmospheric pressure.

The examples below describe the process without restricting it:

EXAMPLES Experimental Part Comparative Example 1a

552.3 g of 2,6-difluorobenzaldehyde are introduced under protective gasinto a column chlorination apparatus (height 60 cm, diameter 5 cm) and2.3 g of 2,2′-azobis(2,4-dimethylvaleronitrile) are added with stirring.The mixture is then heated to 67° C. internal temperature and, in thecourse of 7 hours, a total of 290 g of chlorine are introduced. Thechlorine is added at a rate of 14 liters/hour. Unreacted chlorine isthen blown out with protecting gas and the reaction mixture is cooled toroom temperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  2.4% (a/a) 2,6-difluorobenzaldehyde monitoring:85.1% (a/a) 2,6-difluorobenzoyl chloride  1.1% (a/a) 2-fluorobenzoylchloride 10.7% (a/a) minor component Conversion rate: 97.6% Selectivity:87.2%

Comparative Example 1b

552.7 g of 2,6-difluorobenzaldehyde are introduced under protecting gasinto a column chlorination apparatus (height 60 cm, diameter 5 cm) and2.3 g of 2,2′-azobis(2,4-dimethylvaleronitrile) are added with stirring.The mixture is then heated to 51° C. internal temperature and, in thecourse of 7 hours, a total of 292 g of chlorine are introduced. Thechlorine is added at a rate of 14 liters/hour. Unreacted chlorine isthen blown out with protecting gas and the reaction mixture is cooled toroom temperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  1.8% (a/a) 2,6-difluorobenzaldehyde monitoring:92.1% (a/a) 2,6-difluorobenzoyl chloride  5.7% (a/a) minor componentConversion rate: 98.2% Selectivity: 93.8%

Example 1

555.2 g of 2,6-difluorobenzaldehyde in 370 g of chlorobenzene areintroduced under protecting gas into a column chlorination apparatus(height 60 cm, diameter 5 cm) and 2.4 g of2,2′-azobis(2,4-dimethylvaleronitrile) are added with stirring. Themixture is then heated to 51° C. internal temperature and, in the courseof 7 hours, a total of 295 g of chlorine are introduced. The chlorine isadded at a rate of 14 liters/hour. Unreacted chlorine is then blown outwith protecting gas and the reaction mixture is cooled to roomtemperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  0.2% (a/a) 2,6-difluorobenzaldehyde monitoring:98.9% (a/a) 2,6-difluorobenzoyl chloride  0.8% (a/a) minor componentConversion rate: 99.8% Selectivity: 99.1% Yield: 96.7%

There then follows the product distillation under reduced pressure via apacked column (height 100 cm, packing Sulzer CY) at a reflux ratio of1:7, 2,6-difluorobenzoyl chloride boiling at a constant 125° C. at 145mbar. The fractionated 2,6-difluorobenzoyl chloride has a purityof >99.5% (a/a).

Comparative Example 2a

249.8 g of 2-fluorobenzaldehyde are introduced under protecting gas intoa 500 ml flask and 0.9 g of 2,2′-azobis(isobutyronitrile) are added withstirring. The mixture is then heated to 59° C. internal temperature andin the course of 8 hours a total of 152 g of chlorine are introduced.The chlorine is added at a rate of 7 liters/hour. Unreacted chlorine isthen blown out with protecting gas and the reaction mixture is cooled toroom temperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  1.5% (a/a) 2-fluorobenzaldehyde monitoring: 65.6%(a/a) 2-fluorobenzoyl chloride 31.0% (a/a) minor component Conversionrate: 98.5% Selectivity: 66.6%

Comparative Example 2b

247.3 g of 2-fluorobenzaldehyde are introduced under protecting gas intoa 500 ml flask and 1.0 g of 2,2′-azobis(2,4-dimethylvaleronitrile) areadded with stirring. The mixture is then heated to 40° C. internaltemperature and in the course of 8 hours a total of 150 g of chlorineare introduced. The chlorine is added at a rate of 7 liters/hour.Unreacted chlorine is then blown out with protecting gas and thereaction mixture is cooled to room temperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  1.7% (a/a) 2-fluorobenzaldehyde monitoring: 85.6%(a/a) 2-fluorobenzoyl chloride 12.6% (a/a) minor component Conversionrate: 98.3% Selectivity: 87.1%

Example 2

248.0 g of 2-fluorobenzaldehyde in 900 g of chlorobenzene are introducedunder protecting gas into a 2 l flask and 1.0 g of2,2′-azobis(2,4-dimethylvaleronitrile) is added with stirring. Themixture is then heated to 40° C. internal temperature, and in the courseof 8 hours a total of 150 g of chlorine are introduced. The chlorine isadded at a rate of 7 liters/hour. Unreacted chlorine is then blown outwith protecting gas and the reaction mixture is cooled to roomtemperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  1.0% (a/a) 2-fluorobenzaldehyde monitoring: 98.4%(a/a) 2-fluorobenzoyl chloride  0.6% (a/a) minor component Conversionrate: 99.0% Selectivity: 99.4%

Comparative Example 3

829.1 g of 4-fluorobenzaldehyde are introduced under protecting gas intoa column chlorination apparatus (height 60 cm, diameter 5 cm; fillinglevel 55 cm) and 2.7 g (0.16 mol percent) of2,2′-azobis(2,4-dimethylvaleronitrile) are added with stirring. Themixture is then heated to 42° C. internal temperature and chlorine isintroduced. The chlorine is added at a rate of 12 liters/hour. Alreadyafter 2.5 hours, a gel-like solid forms with vigorous foaming, whichleads to the introduction of chlorine needing to be terminated after 13hours.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate 10.7% (a/a) 4-fluorobenzaldehyde monitoring: 66.2%(a/a) 4-fluorobenzoyl chloride 22.2% (a/a) minor component Conversionrate: 89.3% Selectivity: 74.1%

Example 3

402.2 g of 4-fluorobenzaldehyde in 400 g of chlorobenzene are introducedunder protecting gas into a column chlorination apparatus (height 60 cm,diameter 5 cm; filling level 55 cm) and 1.3 g (0.16 mol percent) of2,2′-azobis(2,4-dimethylvaleronitrile) are added with stirring. Themixture is then heated to 42° C. internal temperature and in the courseof 7 hours a total of 240 g of chlorine are introduced. The chlorine isadded at a rate of 11 liters/hour. Unreacted chlorine is then blown outwith protecting gas and the reaction mixture is cooled to roomtemperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  0.5% (a/a) 4-fluorobenzaldehyde monitoring: 97.1%(a/a) 4-fluorobenzoyl chloride  2.4% (a/a) minor component Conversionrate: 99.5% Selectivity: 97.6% Yield: 95.3%

The product is then distilled under reduced pressure via a packed column(height 100 cm, packing Sulzer CY) at a reflux ratio of 1:15, with4-fluorobenzoyl chloride boiling at a constant 94° C. at 40 mbar. Thefractionated 4-fluorobenzoyl chloride has a purity of >99.5% (a/a).

Example 4

310 g of 2-chlorobenzaldehyde in 300 g of chlorobenzene are introducedunder protecting gas into a 1 l flask and 1.1 g of2,2′-azobis(2,4-dimethylvaleronitrile) are added with stirring. Themixture is then heated to 41° C. internal temperature and, in the courseof 7 hours, a total of 164 g of chlorine are introduced. The chlorine isadded at a rate of 8 liters/hour. Unreacted chlorine is then blown outwith protecting gas and the reaction mixture is cooled to roomtemperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  5.0% (a/a) 2-chlorobenzaldehyde monitoring: 93.0%(a/a) 2-chlorobenzoyl chloride  1.1% (a/a) minor component Conversionrate: 95.0% Selectivity: 97.9%

Example 5

200.4 g of 2,6-dichlorobenzaldehyde in 650 g of chlorobenzene areintroduced under protecting gas into a column chlorination apparatus(height 60 cm, diameter 5 cm) and 1.2 g of 2,2′-azobis(isobutyronitrile)are added with stirring. The mixture is then heated to 80° C. internaltemperature and, in the course of 6 hours, a total of 85 g of chlorineare introduced. The chlorine is added at the rate of 5 liters/hour.Unreacted chlorine is then blown out with protecting gas and thereaction mixture is cooled to room temperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  0.1% (a/a) 2,6-dichlorobenzaldehyde monitoring:99.0% (a/a) 2,6-dichlorobenzoyl chloride  0.9% (a/a) minor componentConversion rate: 99.9% Selectivity: 99.1%

Example 6

200.6 g of 2-chloro-6-fluorobenzaldehyde in 600 g of chlorobenzene areintroduced under protecting gas in to a column chlorination apparatus(height 60 cm, diameter 5 cm) and 1.0 g of 2,2′-azobis(isobutyronitrile)is added with stirring. The mixture is then heated to 70° C. internaltemperature and, in the course of 7 hours, a total of 95 g of chlorineare introduced. The chlorine is added at a rate of 5 liters/hour.Unreacted chlorine is then blown out with protecting gas and thereaction mixture is cooled to room temperature.

The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate  0.2% (a/a) 2-chloro-6-fluorobenzaldehyde monitoring:98.4% (a/a) 2-chloro-6-fluorobenzoyl chloride  1.2% (a/a) minorcomponent Conversion rate: 99.8% Selectivity: 98.6%

Example 7

50.1 g of 2-chloro-5-nitrobenzaldehyde in 200 g of chlorobenzene areintroduced under protecting gas into a 500 ml flask and 0.6 g of2,2′-azobis(isobutyronitrile) is added with stirring. The mixture isthen heated to 80° C. internal temperature and, in the course of 3hours, a total of 20 g of chlorine are introduced. The chlorine is addedat a rate of 3 liters/hour. Unreacted chlorine is then blown out withprotecting gas and the reaction mixture is cooled to room temperature.The progress of the reaction is monitored by gas-chromatographicanalysis (GC).

GC conversion rate 55.1% (a/a) 2-chloro-6-nitrobenzaldehyde monitoring:42.3% (a/a) 2-chloro-6-nitrobenzoyl chloride  1.6% (a/a) minor componentConversion rate: 44.9% Selectivity: 94.2%Examples Without Inert Gas

Inert gas was used solely after the reaction for blowing out unreactedchlorine.

Example 8

In a column chlorination apparatus (height 60 cm, diameter 5 cm) 555 g2,6-difluoro-benzaldehyde are introduced in 370 g chlorobenzene and 2.4g 2,2′azobis(2,4 dimethylvaleronitrile) are added with stirring. Themixture is then heated to 50° C. (interior temperature), and, in thecourse of 7 hours, a total of 295 g chlorine are introduced. TheChlorine is added at a rate of 14 litres/hour. Unreacted chlorine isthen blown out with dry nitrogen and the reaction is cooled to roomtemperature. The progress is monitored by gas-chromatographic analysis(GC).

GC conversion  0.6% (a/a) 2,6-difluorobenzaldehyde rate monitoring:98.1% (a/a) 2,6-difluorobenzoyl chloride  0.8% (a/a) minor componentConversion rate: 99.4% Selectivity: 98.7%

The product is then distilled under a vacuum via a packed column (height100 cm, packing Sulzer CY) at a reflux ratio of 1:7,2,6-difluoro-benzoyl chloride boiling at a constant 125° C. at 145 mbar.The fractionated 2,6-difluor-benzoyl chloride has a purity of >99.5%(a/a). The yield is 96.7%.

Example 9

248.1 g of 2-fluorobenzaldehyde and 1.0 g of 2,2′-azobis(2,4dimethylvaleronitrile) are introduced into a 21 flask with 900 gchlorobenzene.

The mixture is then heated to 40° C. (interior temperature), and, in thecourse of 8 hours, a total of 150 g chlorine are introduced. Thechlorine is added at a rate of 7 litres/hour. The progress is monitoredby GC.

GC conversion  0.8% (a/a) 2-Fluorobenzaldehyde rate monitoring: 97.9%(a/a) 2-Fluorobenzoylchloride  0.9% (a/a) minor component Conversionrate: 99.2% Selectivity: 98.7%

Example 10

In a column chlorination apparatus (height 60 cm, diameter 5 cm) 401.9 g4-fluoro-benzaldehyde are introduced in 400 g chlorobenzene and 1.2 g2,2′-azobis(2,4 dimethylvaleronitrile) are added with stirring. Themixture is then heated to 41° C. (interior temperature), and, in thecourse of 7 hours, a total of 250 g chlorine are introduced. Thechlorine is added at a rate of 12 litres/hour. The progress is monitoredby gas-chromatographic analysis (GC).

GC conversion  0.6% (a/a) 4-fluorobenzaldehyde rate monitoring: 96.5%(a/a) 4-fluorobenzoyl chloride  2.4% (a/a) minor component Conversionrate: 95.7% Selectivity: 97.3% Yield: 93.5%

Example 11

312 g of 2-chlorobenzaldehyde and 300 g of chlorobenzene are introducedinto a 11 flask and 1.1 g of 2,2′-azobis(2,4 dimethylvaleronitril) areadded with stirring. The mixture is then heated to 43° C. (interiortemperature), and, in the course of 7 hours, a total of 169 g chlorineare introduced. The Chlorine is added at a rate of 9 litres/hour. Theprogress is monitored by GC. After conversion the unreacted cloride isremoved from the product via a vacuum and separated byvacuum-distillation.

GC conversion  4.3% (a/a) 2-chlorobenzaldehyde rate monitoring: 93.1%(a/a) 2-chlorobenzoyl chloride  1.3% (a/a) minor component Conversionrate: 95.7% Selectivity: 97.3% Yield: 93.5%

Example 12

In a column chlorination apparatus (height 60 cm, diameter 5 cm) 200 g2,6-dicloro-benzaldehyde are introduced in 650 g chlorobenzene and 1.2 g2,2′ azobis(isobutyronitrile) are added with stirring. The mixture isthen heated to 80° C. (interior temperature), and, in the course of 6hours, a total of 89 g chlorine are introduced. The Chlorine is added ata rate of 6 litres/hour. Unreacted chlorine is then blown out with drynitrogen and the reaction is cooled to room temperature. The progress ismonitored by gas-chromatographic analysis (GC).

GC conversion  0.1% (a/a) 2,6-difluorobenzaldehyde rate monitoring:98.5% (a/a) 2,6-difluorobenzoyl chloride  0.8% (a/a) minor componentConversion rate: 99.9% Selectivity: 98.6%

1. A process for preparing substituted berizoyl chlorides of the formula(1)

where R, x and y have the meaning given below, which comprises heatingin the presence of a chlorinating agent and reacting a benzaldehyde ofthe formula (2)

where R, independently of each other, is identical or different and is aphenyl radical that is substituted by halogen, NO₂, CN, or as halogen,NO₂, CN, NR′₂, OR′, SO₂R′, SO₂OR′, COR′ or CO₂R′, where R′ is anunbranched or branched C₁-C₁₀ alkyl radical, an unsubstituted phenylradical or a phenyl radical which is substituted by halogen, NO₂, CN,(C₁-C₄)alkyl or (C₁-C₄)alkoxy, x is 1 or 2 and y is 1, 2 or 3, where ifR is halogen, then all halogens are identical or if R is different, thenonly one R may be a halogen or all the R halogens are identical, and oneor more R is selected from the group of: NO₂, CN, (C₁-C₄)alkyl or(C₁-C₄)alkoxy; with said chlorinating agent in the presence of afree-radical initiator and a solvent, in the absence of an inertdilution gas, at a reaction temperature from −20 to ×200° C.
 2. Theprocess as claimed in claim 1, wherein the benzaldehyde of the formula(2) is used, where R independently of each other is identical ordifferent and is halogen, NO₂, CN, NR′₂, OR′, SO₂R′, SO₂OR′, COR′ orCO₂R′, where R′ is an unbranchod or branched C₁-C₄ alkyl radical or anunsubstituted phenyl radical, if R is halogen, then all halogens areidentical or if R is different, then only one R may be a halogen or allthe R halogens are identical and one or R is selected from the group of:NO₂, CN, (C₁-C₄)alkyl or (C₁-C₄)alkoxy.
 3. The process as claimed inclaim 1, wherein a benzaldehyde (2) is used where x is
 1. 4. The processas claimed in claim 1, wherein a benzaldehyde (2) is used where at leastone of the radicals R is a halogen in an ortho position to an aldehydegroup.
 5. The process as claimed in claim 1, wherein a benzaldehyde (2)is used where R independently of each other is identical and is F, Cl orNO₂, or R independently of each other is different and is F or Cl withNO₂ x is 1 and at least one of the radicals R is an F or Cl in orthoposition to the aldehyde group, where if R is halogen, then all halogensare identical or if R is different, then only one R may be a halogen orall the R halogens are identical and one or more R is selected from thegroup consisting of: NO₂, CN, (C₁-C₄)alkyl, (C₁-C₄)alkoxy, and mixturesthereof.
 6. The process as claimed in claim 1, wherein the chlorinatingagent is selected from the group consisting of Cl₂, SOCl₂, SO₂Cl₂, PCl₃,POCl₃, PCl₅, SbCl₅, ICl, ICl₃, SCl₂, S₂Cl₂, MnCI₄, (C₁-C₄)alkylhypochlorite, CCl₄, N-chlorosuccinmide, and mixtures thereof.
 7. Theprocess as claimed in claim 1, wherein the chlorinating agent isselected from the group consisting of Cl₂, SOCl₂, SO₂Cl₂, and mixturesthereof.
 8. The process as claimed in claim 1, wherein the free-radicalinitiator used is an organic peroxide or an organic azo compound or amixture of the same.
 9. The process as claimed in claim 1, wherein thefree-radical initiator is selected from the group consisting of2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobis(isobutyronitrile),2,2-azobis(4-methoxy-2,4-dimethylvaleronitrile), and mixtures thereof.10. The process as claimed in claim 1, wherein the solvent is selectedfrom the group consisting of a monochlorinated or polychlorinatedaliphatic or aromatic hydrocarbon, and mixtures thereof.
 11. The processas claimed in claim 1, wherein the solvent is selected from the groupconsisting of chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene,1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene,1,3,5-trichlorobenzene, 2-chlorotoluene, 3-chlorotoluene,4-chlorotoluene, and mixtures thereof.
 12. The process as claimed inclaim 1, wherein the reaction temperature is 0 to 120° C.
 13. Theprocess as claimed in claim 1, wherein the reaction temperature is from20 to 90° C.
 14. A process for preparing substituted benzoyl chloridesof the formula (1)

where R, x and y have the meaning given below, which comprises heatingin the presence of a chlorinating agent and reacting a benzaldehyde ofthe formula (2)

where R, independently of each other, is identical or different and is aphenyl radical that is substituted by halogen, NO₂, CN, or is halogen,NO₂, CN, NR′₂, OR′, SO₂R′, SO₂OR′, COR′ or CO₂R′, where R′ is anunbranched or branched C₁-C₁₀ alkyl radical, an unsubstituted phenylradical or a phenyl radical which is substituted by halogen, NO₂, CN,(C₁-C₄) alkyl or (C₁-C₄)alkoxy, x is 1 or 2 and y is 1, 2 or 3, withchlorinating agent in the presence of an inert dilution gas, in thepresence of a free-radical initiator, and a solvent at a reactiontemperature from −20 to ×200° C.
 15. The process as claimed in claim 14,wherein the benzaldehyde of the formula (2) is used, where Rindependently of each other is identical or different and is halogen,NO₂, CN, NR′₂, OR′, SO₂R′, SO₂OR′, COR′ or CO₂R′, where R′ is anunbranched or branched C₁-C₄ alkyl radical or an unsubstituted phenylradical, if R is halogen, then all halogens are identical or if R isdifferent, then only one R may be a halogen and one or more othercompounds selected from the group consisting of NO₂, CN, (C₁-C₄)alkyl,(C₁-C₄)alkoxy, and mixtures thereof.
 16. The process as claimed in claim14, wherein a benzaldehyde (2) is used where x is 1 and where at leastone of the radicals R is a halogen in an ortho position to an aldehydegroup.